This invention relates to an apparatus for winding up a strip of thin material such as paper, plastic film, and laminated material into a roll.
Japanese Unexamined Patent Publication No. 5-270704 discloses a winding apparatus in which a strip of thin material is wound about a winding shaft by rotating the winding shaft. This winding apparatus comprises a crown touch roller having a crown portion or bulged surface in an axially intermediate portion thereof and a spur touch roller having a straight outer surface parallel with the axis thereof. The crown touch roller and the spur touch roller are rotated while being brought into pressing contact with the thin material being wound up by the shaft.
The combination of the crown and spur touch rollers constitutes an arrangement to expel the air from rolled layers and prevent the air from coming into rolled layers. Specifically, the bulged intermediate portion of the crown touch roller comes into pressing contact with an axially intermediate portion of the rolled material to expel the air from the rolled layers. Also, the spur touch roller comes into pressing contact with the rolled material over the entire width to further expel the air from rolled layers.
The conventional apparatus can prevent a poor roll of thin material containing the air in layers. However, this apparatus cannot prevent a slip between rolled layers which is liable to occur in the case of slippery thin material such as plastic film.
More specifically, in winding up a thin material, the so-called "layer slip" is liable to occur that rolled layers are slipped one over another during the winding operation, particularly in a radially middle portion of the roll. This has been understood to occur when the tension exerting on the thin material 1 is larger than a frictional resistance between rolled layers. Such layer slip results in a poor roll of thin material having irregularities on its side end surfaces.
In order to prevent the layer slip, there have been taken a countermeasure of controlling the drive motor of driving the winding shaft to reduce step-by-step the tension on the thin material being wound up about the shaft, and another countermeasure of controlling the drive motor in accordance with a pre-set program to linearly reduce the tension on the thin material in accordance with an increase in the diameter of the rolled thin material. However, in the case of winding up a strip of thin material having a small friction coefficient, there has still been the difficulty in controlling the drive motor to completely prevent the layer slip to ensure a smooth side end surface of a finished roll of thin material.